Increasing the ion content of the air within a room can be desirable for a variety of reasons. For example, a high negative ion content freshens the air and has beneficial physiological effects on persons who breathe the air. Air ions of either polarity act to remove dust, pollens, smoke and the like by imparting an electrical charge to such particulates. The charged particles are electrostatically attracted to walls or other nearby surfaces and tend to cling to such surfaces.
Some usages of air ionizers require production of both positive and negative ions. Most notably it has been found that a high concentration of both types of ion acts to suppress accumulations of static electricity on objects in a room. Static electrical charges attract air ions of the opposite polarity and the attracted ions then neutralize the static charges. This can be of particular value in certain industrial operations such as in the clean rooms where microchips or other miniaturized electronic components are manufactured. Accumulations of static charge attract contaminants to such products and may also directly damage a microchip or the like.
An advantageous type of ionizing device has sharply pointed electrodes to which high voltages of the order of several thousand volts are applied and which are exposed to the ambient air. Positive and negative high voltages are applied to separate electrodes or are alternately applied to the same electrode. The resulting intense electrical field near the pointed end of the electrode converts the nearby molecules of the constituent gases of air into positive and negative ions. Ions with a polarity opposite to that of the high voltage are attracted to the electrode and neutralized. Ions of the same polarity as the high voltage are repelled by the electrode and by each other and disperse outward into the surrounding air. Dispersal of the ions is usually accelerated by directing an airflow through the electrode region and out into the room.
It is usually desirable to produce a predetermined ratio of positive to negative ions and in many cases such ions are to be produced in equal numbers. Such balancing can be accomplished initially by measuring the ion content of the air flow with an ion detector and adjusting the high voltage on one or more of the electrodes as needed to achieve the desired balance.
The initial balancing of positive and negative ion production does not usually persist over a period of time. Various factors, such as electrode erosion or utility line voltage fluctuations, can cause a change in the ratio of positive ion production to negative ion production. This can have a very detrimental effect. An excess of one type of ion relative to the other can cause the apparatus to impart electrostatic charge to objects in a room rather than acting to suppress such charge.
The problem has heretofore typically been dealt with by disposing an air ion sensor in the air flow path to detect any change in the ratio of positive to negative ions. The sensor is coupled to a feedback system which responds to changes in the sensor signal by adjusting electrode voltages or the durations of periods of electrode energization as needed to re-establish the original balance of positive and negative ion production.
Such ion sensors, feedback components and voltage adjusting means add substantially to the cost, complexity and bulk of the ionizing apparatus. An air ionizer which inherently maintains a balanced production of positive and negative ion without such complications would clearly be advantageous.
The positive and negative ions in the air flow should be thoroughly intermixed if the apparatus is to suppress static charges on objects rather than creating such charges. This condition is not met immediately since the ions of different polarity are produced at separated electrodes or at different time periods at the same electrode. Such intermixing does occur gradually as the airflow progresses away from the ioning apparatus but it has heretofore been necessary to keep the ionizer a sizable distance away from objects that are to be protected to avoid subjecting the objects to incompletely mixed concentrations of ions of one polarity. It would be more convenient in many instances if the ionizer could be closer to the objects on which static charge is to be suppressed.
The present invention is directed to overcoming one or more of the problems discussed above.